$\dfrac{9}{3} - \dfrac{8}{5} = {?}$
Answer: $ = {\dfrac{9 \times 5}{3 \times 5}} - {\dfrac{8 \times 3}{5 \times 3}} $ $ = {\dfrac{45}{15}} - {\dfrac{24}{15}} $ $ = \dfrac{{45} - {24}}{15} $ $ = \dfrac{21}{15}$